Taxonomy of the fossil marine diatom resting spore genus Odontotropis

Abstract

This article describes the taxonomy of Odontotropis Grunow including nine taxa with two new species (O. circularis Wise, O. danicus Debes ex Hustedt, O. carinata Grunow, O. arctica Suto sp. nov., O. reticulata Suto sp. nov., O. cristata Grunow, O. galeonis Hanna, O. hyalina Witt and O. birostrata Pantocsek) mostly from Arctic core materials (Integrated Ocean Drilling Program, IODP Expedition 302), in addition to a synonymy list, light and scanning electron microscopy observations and several key references for each taxon. This genus is characterized by having a strongly vaulted frustule, a boat-shaped or circular outline with a sharp carina around the margin and a long history from the Cretaceous to the middle Eocene. The resting spores of Odontotropis may have had a similar ecological strategy to that of dinoflagellate cysts rather than Chaetoceros resting spores. The Odontotropis resting spore extinction occurred before the Eocene/Oligocene Event of Suto which was characterized by a Chaetoceros resting spore explosive diversification, an increase in abundance, and a decrease in valve size. These changes indicate that coastal conditions became unstable, whereby there was a regular seasonal environmental change involving the depletion and sporadic supply of nutrients, conditions more favorable to Chaetoceros resting spores than to dinoflagellate cysts.

Keywords:

• Odontotropis: fossil diatoms
• resting spores
• IODP Expedition 302
• Arctic Coring Expedition
• ACEX

Acknowledgements

We thank the co-chief scientists Jan Backman (Stockholm University) and Kathryn Moran (University of Rhode Island), and the scientific party of IODP Leg 302 ACEX as well as the captain and crew who provided the opportunity for us to sample the sediments on board the R/V Oden. We wish to thank Kota Katsuki (Kochi University), Nalân Koç and Catherine E. Stickley (Norwegian Polar Institute) for invaluable discussions. Special thanks are given to Kozo Takahashi (Kyushu University) and Jo-naotaro Onodera (JAMSTEC) who provided sieved samples and gave numerous suggestions. We also thank Yoshihiro Tanimura (National Science Museum, Tokyo), who kindly curated the type specimens described in this paper. We are grateful to Elisabeth Fourtanier (California Academy of Science) and Patrick Kociolek (University of Colorado) for providing valuable discussion and copies of some old papers. This research used samples and data provided by the Integrated Ocean Drilling Program (IODP). This work was partially supported by JSPS Grant-in-Aid for Young Scientists (B) Project No. 20740299.